This invention relates to a light-weight, lustless surface, abrasion resistant, soft vinyl chloride resin composition.
Soft vinyl chloride resins are superior in physical and chemical properties, readily processable and relatively cheap. Thus they have been broadly used for sundries of daily use, automobile components, etc. in the form of various molded products and further leather, sheet, etc. However, the specific gravities of soft vinyl chloride resins are in the range of 1.2 to 1.5, that is, when compared with other general-purpose resins, they are as high as 1.3 to 1.6 times those of polypropylene or 2 to 2.5 times those of foamed polyurethane of RIM process. This has come to be regarded as a serious defect in the application field of automobile parts where it has been aimed to make the components light-weight for energy saving.
As for processes for making soft vinyl chloride resins light-weight, a foaming process using chemical foaming agents has been generally employed, but this process has various drawbacks in productivity and economy such that the molding cycle is long; the ranges of processing conditions are narrow; foams are readily broken; the product yield is inferior; it is impossible to regenerate and reuse waste articles; etc.
As for other processes for making soft vinyl chloride resins light-weight, a process of blending microballoons such as glass balloon as a filler is known. However, such a filler is intrinsically deficient in adhesion to vinyl chloride resins; molded products obtained by using resins having such a filler blended therein are reduced in mechanical strengths or the filler is readily peeled off from the surface of molded products during their use, to make the abrasion resistance inferior; thus in order to be freed of such defects, it becomes necessary to simultaneously use a coupling agent such as silane compounds; hence various problems have been raised in operability and economy.
On the other hand, in the application field of automobile parts, molded products having a lusterless surface have come to be desired. As for processes for producing lusterless molded products, there have been proposed (1) a process of applying a lusterless paint onto the surface of molded products; (2) a process of providing uneven surface for molded products by means of a metal mold or roll having projections and depressions on its surface; (3) process of blending a high molecular weight luster-preventing agent such as cross-linked acrylic resins; (4) a process of using a vinyl chloride resin having a high average degree of polymerization; (5) a process of blending an inorganic filler such as calcium carbonate; etc., but any of these processes have the following drawbacks and are unsatisfactory:
According to the process (1) or (2), the lusterless state of surface is easily lost by abrasion. According to the process (3), the effect to prevent luster is small, and if the agent is blended in a large amount, uneven luster is formed on the surface of molded products. According to the process (5), a luster preventing effect is exhibited, but the specific gravity increases and the mechanical properties, particularly the abrasion resistance, are much reduced and further the surface is liable to be injured. It may be considered to simultaneously employ the processes (1) and (2), that is, to overlay a lusterless paint upon an embossed surface, to thereby cause the resulting surface to retain the lusterless state for a long time, but the cost increases due to increase in processing steps; hence such process is not practical.
In order to solve the above problems directed to soft vinyl chloride resins, the present inventors have made extensive research, and as a result, have found that when a specified filler and a plasticizer are blended with a specified vinyl chloride copolymer, the resulting soft vinyl chloride resin composition has a light-weight, can retain a lusterless state for a long term, and has a superior abrasion resistance.